CHARACTERIZATION OF THE DOUBLE GENOME STRUCTURE OF MODERN SUGARCANE CULTIVARS (SACCHARUM SPP) BY MOLECULAR CYTOGENETICS

Cultivated sugarcane clones (Saccharum spp., 2n = 100 to 130) are deri ved from complex interspecific hybridizations between the species S. o fficinarum and S. spontaneum. Using comparative genomic DNA in situ hy bridization, we demonstrated that it is possible to distinguish the ch romosomes contributed by these two species in an interspecific F1 hybr id and a cultivated clone, R570. In the interspecific F1 studied, we o bserved n+n transmission of the parental chromosomes instead of the pe culiar 2n+n transmission usually described in such crosses. Among the chromosomes of cultivar R570 (2n = 107-115) about 10% were identified as originating from S. spontaneum and about 10% were identified as rec ombinant chromosomes between the two species S. officinarum and S. spo ntaneum. This demonstrated for the first time the occurrence of recomb ination between the chromosomes of these two species. The rDNA sites w ere located by in situ hybridization in these two species and the cult ivar R570. This supported different basic chromosome numbers and chrom osome structural differences between the two species and provided a fi rst bridge between physical and genetical mapping in sugarcane.